1. Field of the Invention
The present invention relates to a flat type vibration motor built into a mobile phone etc., more particularly relates to its rotor structure.
2. Description of the Related Art
In the past, a flat type vibration motor has been provided with a stainless steel disk-shaped base plate on which one end of a shaft is press-fitted into a burring part, a closed-bottom cylindrically shaped cover case made of stainless steel in which an open part is closed by the base plate and the other end of the shaft is inserted into a shaft mounting hole, a rotor frame supported to be able to rotate via a slide bearing through which the shaft runs and having an axial direction field-type rotary magnet and an eccentric weight, and a flexible printed circuit board superposed on the base plate and mounting a plurality of electronic components such as air core coils and a current control IC. The rotor frame has the burring part attached to the slide bearing and a disk part having a ring-shaped rotary magnet and a fan-shaped eccentric weight at the outer circumferential side of the rotary magnet.
As related art, there is Japanese Patent Publication (A) No. 2008-182837 (FIG. 2 and FIG. 3).
In the above flat type vibration motor, the high specific gravity alloy fan-shaped eccentric weight is integrally joined with the disk part of the rotor frame by spot welding at several points, so easily is corroded along with the elapse of time. Further, the slide bearing to which the burring part of the rotor frame is attached has a ring-shaped projection for swaging use at its outer circumferential surface, so a specially shaped slide bearing is required and higher cost is incurred.